The compatibility of mycorrhizal fungi with the early growth stage of orchids is essential for their growth. In this study, the compatibility and promotion effects of 14 Tulasnella strains from different hosts were studied by co-culturing them with the protocorms of Dendrobium crepidatum, which has high ornamental and economic value in China. The ITS–LSU–SSU–TEF combined sequence analysis divided the 14 strains into three clades belonging to Tulasnella calospora (clades A and B) and Tulasnella asymmetrica (clade C). All the strains were compatible with D. crepidatum protocorms within 90 d of the co-culture. Strain T12 in Clade A had a significantly higher (p < 0.05) effect on the biomass and morphology of D. crepidatum, and strain T13 in Clade C had a significantly lower (p < 0.05) effect than the other strains. Through morphological principal component analysis, we constructed a hierarchical cluster analysis tree, which was consistent with the phylogenetic tree of these 14 strains at the clade level. Orthogonal partial least squares-discriminant analysis showed that these strains have an important effect on the plant height, root number, and length of D. crepidatum. The findings of this study will contribute to the identification of Tulasnella strains, conservation of D. crepidatum resources, and commercial utilization of mycorrhizal technology.